It is not uncommon for thrombi to form in a vessel. Sometimes, such clots are harmlessly dissolved in the blood stream. At other times, however, such clots may lodge in a blood vessel, where they can partially or completely occlude the flow of blood. If the partially or completely occluded vessel feeds blood to sensitive tissue such as, the brain, lungs or heart, for example, serious tissue damage may result. Such ischemic events may also be exacerbated by atherosclerosis, a vascular disease that causes the vessels to become narrowed and tortuous. The narrowing or increased tortuousness of the vessel may, in certain circumstances, lead to the formation of atherosclerotic plaque, which can cause further complications in the body. Embolectomy devices such as inflatable catheters and clot pullers are used in a variety of applications to remove blood clots or other foreign bodies from a blood vessel such as an artery or vein.
In an embolectomy procedure for removing a blood clot from a patient's blood vessel, a delivery catheter or sheath is typically inserted percutaneously into the patient's vasculature, e.g. via the femoral, jugular or antecubital veins, by so-called minimally invasive techniques, and advanced to a target site within the vessel containing the clot. To ascertain the precise location of the blood clot within the vessel, radiopaque dye may be injected into the vessel permitting the occluded blood vessel to be radiographically visualized with the aid of a fluoroscope. For example, a Fogarty catheter or other suitable delivery device may be used to transport the embolectomy device in a collapsed position distal the site of the clot. Many delivery devices include sheaths or catheters, and delivery members fixed to the embolectomy device to push and pull embolectomy device through the sheaths and catheters. Catheter and delivery members may be configured to be bent without breaking while navigating through tortuous vasculature. The catheter is delivered to the site where it is required through the patient's skin or by a “cut down” technique in which the blood vessel concerned is exposed by minor surgical means.
An embolectomy device is compressed radially inwards and delivered through the catheter for positioning adjacent to the clot to be removed. The embolectomy device is then pushed distally relative to the catheter, or the catheter is withdrawn proximally relative to the embolectomy device (or some of each), in order to deploy the embolectomy device out of the catheter and into the blood vessel, allowing the no-longer radially constrained embolectomy device to radially expand to a predetermined diameter within the blood vessel. The expanded embolectomy device is then urged in a proximal direction to ensnare and remove the clot from the vessel wall. A wire basket, coil, membrane or other collector element can be used to capture the clot as it is dislodged from the vessel wall. Clot capture strategies include increased axial friction from radially expansile force, snaring/encapsulation/entrapment, integration, and envelopment. The characteristics of the clot, the vascular location and the removal device determine the strategy or combination of strategies used in each clot removal. Once captured by the collector element, the embolectomy device and captured blood clot are then loaded into a retrieval device and withdrawn from the patient's body. In certain applications, the removal of the foreign object within the vessel may cause emboli to migrate downstream and enter other branching passageways within the body. To prevent migration of emboli downstream, it may be necessary to temporarily impede or obstruct the flow of blood distal to the therapeutic site while retrieving the embolectomy device.
Embolectomy devices are generally tubular devices for insertion into body lumens. However, it should be noted that embolectomy may be provided in a wide variety of sizes and shapes. Self-expanding embolectomy device expand when unconstrained, without requiring any further input. A self-expanding embolectomy device may be biased so as to expand upon release from the delivery catheter and/or include a shape-memory component which allows the stent to expand upon exposure to a predetermined condition. Self-expanding embolectomy device are biased to an expanded configuration. Embolectomy devices can be made from a variety of materials, including metals and polymers. Embolectomy devices can be made from shape memory materials, such as shape memory metals (e.g., Nitinol) and polymers (e.g., polyurethane). Such shape memory embolectomy devices can be induced (e.g., by temperature, electrical or magnetic field or light) to take on a shape (e.g., a radially expanded shape) after delivery to a treatment site. Other embolectomy device materials include stainless steel, and Elgiloy.
Embolectomy devices are typically cylindrical scaffolds formed from a set of elongate elements (i.e., struts). The struts can interconnect in a repeating pattern or in a random manner. The scaffolding can be woven from wires, cut out of tubes, or cut out of sheets of material that are subsequently rolled into a tube. Tubes and sheets from which stents are cut as also known as stent “preforms.” The manner in which an embolectomy device's struts interconnect determines its longitudinal and radial rigidity and flexibility. Radial rigidity is needed to provide the radial force needed to engage the clot, but radial flexibility is needed to facilitate radial compression of a stent for delivery. Longitudinal rigidity is needed to pull an engaged clot from the vessel, but longitudinal flexibility is needed to facilitate delivery of the stent (e.g., through tortuous vasculature). Embolectomy device patterns are typically designed to maintain an optimal balance between longitudinal and radial rigidity and flexibility for the embolectomy device.
Embolectomy devices can be cut from tubes and sheets using a variety of techniques, including laser cutting or etching a pattern onto a tube or sheet to form struts from the remaining material. Lasers cutting or etching may be performed on a sheet, which is then rolled into a tube, or a desired pattern may be directly cut or etched into a tube. Other techniques involve forming a desired pattern into a sheet or a tube by chemical etching or electrical discharge machining. Laser cutting of stents, which are structurally similar to embolectomy devices, has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. Nos. 5,922,005 and 5,906,759 to Richter and U.S. Pat. No. 6,563,080 to Shapovalov, the entire disclosures of which are incorporated herein by reference, as though set forth in full. Embolectomy devices may also include components that are welded, bonded or otherwise engaged to one another.